This invention relates to an aromatics complex flow scheme, which is a combination of process units that can be used to convert naphtha into basic petrochemical intermediates of benzene, toluene, and xylene. Based on a metal catalyzed transalkylation process that handles unextracted toluene and heavier aromatics and an olefin saturation process, the improved flow scheme removes items of equipment and processing steps, such as a reformate splitter column and a heavy aromatics column, resulting in significant economic benefits when producing para-xylene.
Most new aromatics complexes are designed to maximize the yield of benzene and para-xylene. Benzene is a versatile petrochemical building block used in many different products based on its derivation including ethylbenzene, cumene, and cyclohexane. Para-xylene is also an important building block, which is used almost is exclusively for the production of polyester fibers, resins, and films formed via terephthalic acid or dimethyl terephthalate intermediates. Accordingly, an aromatics complex may be configured in many different ways depending on the desired products, available feedstocks, and investment capital available. A wide range of options permits flexibility in varying the product slate balance of benzene and para-xylene to meet downstream processing requirements.
A prior art aromatics complex flow scheme has been disclosed by Meyers in the Handbook of Petroleum Refining Processes, 2d. Edition in 1997 by McGraw-Hill.
U.S. Pat. No. 3,996,305 to Berger discloses a fractionation scheme primarily directed to transalkylation of toluene and C9 alkylaromatics in order to produce benzene and xylene. The transalkylation process is also combined with an aromatics extraction process. The fractionation scheme includes a single column with two streams entering and with three streams exiting the column for integrated economic benefits.
U.S. Pat. No. 4,341,914 to Berger discloses a transalkylation process with recycle of C10 alkylaromatics in order to increase yield of xylenes from the process. The transalkylation process is also preferably integrated with a para-xylene separation zone and a xylene isomerization zone operated as a continuous loop receiving mixed xylenes form the transalkylation zone feedstock and effluent fractionation zones.
U.S. Pat. No. 4,642,406 to Schmidt discloses a high severity process for xylene production that employs a transalkylation zone that simultaneously performs as an isomerization zone over a nonmetal catalyst. High quality benzene is produced along with a mixture of xylenes, which allows para-xylene to be separated by absorptive separation from the mixture with the isomer-depleted stream being passed back to the transalkylation zone.
U.S. Pat. No. 5,417,844 to Boitiaux et al. discloses a process for the selective dehydrogenation of olefins in steam cracking petrol in the presence of a nickel catalyst and is characterized in that prior to the use of the catalyst, a sulfur-containing organic compound is incorporated into the catalyst outside of the reactor prior to use.
U.S. Pat. No. 5,658,453 to Russ et al. discloses an integrated reforming and olefin saturation process. The olefin saturation reaction uses a mixed vapor phase with addition of hydrogen gas to a reformate liquid in contact with a refractory inorganic oxide containing preferably a platinum-group metal and optionally a metal modifier.
U.S. Pat. No. 5,763,720 to Buchanan et al. discloses a transalkylation process for producing benzene and xylenes by contacting a C9+ alkylaromatics with benzene and/or toluene over a catalyst comprising a zeolite such as ZSM-12 and a hydrogenation noble metal such as platinum. Sulfur or stream is used to treat the catalyst.
U.S. Pat. No. 5,847,256 to Ichioka et al. discloses a process for producing xylene from a feedstock containing C9 alkylaromatics with the aid of a catalyst with a Is zeolite that is preferably mordenite and with a metal that is preferably rhenium.
An aromatics complex flow scheme with an enabled transalkylation process requires stabilization of a transalkylation catalyst through the introduction of a metal function. Enabling a transalkylation process to handle both C10 alkylaromatics and unextracted toluene permits the following flow scheme improvements to be realized. By using toluene without first passing it to an extraction unit, the flow scheme omits a reformate-splitter column. The concomitantly smaller capacity extraction unit is moved to the overhead of a benzene column. By only extracting benzene, simple extractive distillation is used, since a more expensive combined liquid-liquid extraction method is only required for heavier contaminants. By using both C9 and C10 alkylaromatics in an enabled transalkylation unit, the flow scheme further omits a heavy aromatics column. A further enhancement to the flow scheme is accomplished through the elimination of clay treaters in favor of selective olefin saturation at the exits of a reforming process unit or of an alkylaromatic isomerization process unit.
Another embodiment of the present invention comprises an apparatus that is based on the process steps, which efficiently converts naphtha into para-xylene.
Additional objects, embodiments and details of this invention can be obtained from the following detailed description of the invention.